Rather than asserting, as seen in #7977.
This shouldn't crash the server in production.
Add unit test that reproduces this scenario
and verifies the internal error exception.
Fixes#7977
Test: unit(release)
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20210201163051.1775536-1-bhalevy@scylladb.com>